1. Field of the Invention
Embodiments of the invention generally relate to a pedestal having a shield for supporting a substrate in a semiconductor processing chamber.
2. Background of the Related Art
In semiconductor substrate processing, the trend towards increasingly smaller feature sizes and linewidths has placed a premium on the ability to mask, etch, and deposit material on a semiconductor workpiece, or substrate, with greater precision. Plasma etching is of particular importance in obtaining critical dimensions less than 0.25 micron.
Typically, etching is accomplished by applying RF power to a working gas supplied to a low pressure processing region over a substrate supported by a support member. The resulting electric field creates a reaction zone in the processing region that excites the working gas into a plasma. The support member is biased to attract ions within the plasma towards the substrate supported thereon. Ions migrate towards a boundary of the plasma adjacent the substrate and accelerate upon leaving the boundary layer. The accelerated ions produce the energy required to remove, or etch, the material from the surface of the substrate. As the accelerated ions can etch other items within the processing chamber, it is important that the plasma be confined to the processing region above the substrate.
FIG. 1 illustrates an exemplary processing chamber 100 that provides for plasma confinement. The processing chamber 100 includes a chamber body 102 having a vertically movable substrate support member 104 disposed therein. The support member 104 generally includes one or more electrodes (not shown) for biasing the substrate. The chamber body 102 generally includes a lid 106, a bottom 108 and sidewalls 110. Coils 112 are disposed proximate the lid 106 and are coupled to a power source 114. An annular shield 116 is coupled to the sidewalls 110 or lid 106 and circumscribes the support member 104. A cover ring 118 is suspended from a J-section 120 of the shield 116 when the support member 104 is in a lowered position.
As the support member 104 is elevated to a processing position as depicted in FIG. 1, the perimeter of the support member 104 contacts the cover ring 118, lifting the cover ring 118 off the shield 116. Since the cover ring 118 and J-section 120 of the shield 116 remain interleaved creating a labyrinth or gap, plasma formed in a process region 122 defined between the support member 104 and the lid 106 does not migrate to a region 124 below the support member 104 where ions leaving the plasma may etch chamber components proximate thereto.
Although utilization of a cover ring lifted by a support member has been successfully commercialized, the use of cover rings in processing chambers utilizing ceramic support members is generally not preferred. Generally, each time the ceramic support member is raised to the processing position, the cover ring impacts the ceramic support member. The repeated impact of the cover ring with a ceramic support member over the course of processing a number of substrates is undesirable due to the brittle nature of ceramic. The ceramic support member is often damaged after repeated impact and may chip, break or generate particles. This leads to premature replacement of the ceramic support member and causes poor processing and increased defect rates.
Therefore, there is a need for an improved method and apparatus for supporting a substrate on a ceramic support member in a processing chamber.